An organic electroluminescence device (hereinafter referred to as an organic EL device) includes an organic compound layer having an emitting layer provided between a pair of electrodes formed on a substrate. The organic EL device is usable in a light-emitting device and a lighting device.
A substrate of a typical organic EL device is a glass substrate. Thus, it is difficult to realize an organic EL device with flexibility. Further, the glass substrate itself is expensive, which results in an increase of the price of the organic EL device.
In order to deal with such problems, for instance, Patent Literature 1 discloses an organic electroluminescence device including a lower electrode, an organic compound layer including an emitting layer, and a back plate that are disposed on a flexible substrate. In Patent Literature 1, the flexible substrate is exemplified by a substrate including an aluminum foil base, an antireflection layer and an insulating layer, the antireflection layer and the insulating layer being disposed on the base. According to Patent Literature 1, such a flexible substrate contributes to improvement in a contrast reduction caused when the organic electroluminescence device is used in a display.
It has also been discussed to employ a metal substrate as a flexible substrate of an organic EL device used in a lighting device.
An electrode and an organic emitting layer of an organic EL device have a thin film thickness. Thus, when a surface of the metal substrate is not smooth, the organic EL device using the metal substrate as the flexible substrate is likely to suffer from a short-circuit between electrodes formed on the substrate, which results in a lowered yield rate. In view of the above, the surface of the metal substrate needs to be smooth, so that the surface of the metal substrate is smoothened by mirror-polishing or by an SOG (Spin On Glass) technique, in which a solution prepared by blending SiO2 in a solvent is applied on a rotating substrate to form a smooth film on the surface of the substrate.
However, it is quite difficult to smoothen a large area of the surface of the metal substrate through mirror-polishing or the SOG technique and thus such methods are not suitable for mass production.
Regarding the smoothness of the surface of the metal substrate, Patent Literature 2 discloses that a nickel-plating layer is formed on the surface of the metal substrate by electroless plating to smoothen the surface. Patent Literature 2 discloses that an organic EL device is provided by sequentially laminating a functional layer, which includes an organic emitting layer, and a cathode layer on a surface of an electroless nickel-plating layer formed on the surface of the metal substrate.